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Rice growers weigh herbicide carryover in '07 management

I have received a number of calls from consultants, county agents and growers about what to grow in fields where Newpath was used on Clearfield rice last year.

According to both university and BASF stewardship recommendations, whenever possible you should rotate Clearfield rice with soybeans or some other crop for purposes of resistance management. This has not been the case for several years in many Arkansas fields. Many of our fields have been in continuous Clearfield since it was introduced.

The lack of Clearfield rice seed (due to the announcement of a contaminant in CL 131 and one lot of hybrid CL rice) has many farmers in a bind.

The official crop rotation for Newpath herbicide to regular rice is 18 months. This rotational interval is for any rate of Newpath, even if only 4 ounces were used for some reason.

The addition of Beyond herbicide to the program does not affect crop rotation. This rotation interval is a real one. There will likely be injury to regular rice at some level if it is planted the year following an application of Newpath.

The active ingredient in Newpath is imazethapyr, which is the same as Pursuit herbicide. The original Pursuit label had a 40-month rotation to rice, which effectively took it out of the Southern soybean herbicide market. In the South we used Scepter, which had a more favorable rotational interval to rice.

Newpath degradation in the soil depends on several things. These include: soil type, drainage, whether or not it was flooded in the winter, soil ph and microbial activity, among other things.

Newpath degradation occurs rapidly at first, then levels out. I have talked to several folks who have sent in soil samples and found around 10 to 20 percent of the Newpath remaining in the soil. This is to be expected. There is a rapid degradation of the first 70 or 80 percent of the compound; the rest takes more time.

This is probably oversimplified, but I never claimed to be a herbicide physiologist. I always advise against testing for herbicide residues in these situations. It is somewhat a waste of money. You know you put it out there, so it is no surprise that it is there.

The results come back in ppm (parts per million), which can be converted to ounces per acre, but then the question still is, “Will it hurt my rice?” No one can say for sure, even if you know the exact ppm left out there!

In general, I have observed anywhere from 0 to 40 percent stunting when regular rice is planted behind Clearfield rice and Newpath herbicide. The severity of damage depends on the rate used, pH of the soil, soil type and winter cultural practices.

For example, using the 6 ounces followed by 6 ounces per acre program — putting the first shot out ppi — on a higher pH soil that is poorly drained or was flooded this winter is a worst case scenario. Using a low seeding rate and planting early would make injury appear worse.